Lead screw stop means



Patented Feb. 14, 1950 UNITED STATES PAT-ENT OFFICE Frank TerdinwandWallace Skidmore,v Seattle, Wash..assignors to. Boeing Airplane Company,a. .corporation of. Delaware .Application JanuaryZS, 1946, Serial No.643,415

(Cl. i4-424.8)

.to :failures oi the-:power transmission .mechanism,

-with resulting inoperation of the 'component Yac- I,tuated by the,leadz screw frequently' causing se'- xrious damage vto ,the ,machine-orvehicle with ,which thev componentl iseqnipped. 'Toio abrupt stopping orarresting ofthe moving elements Vmay alsoresult indamage tothe screw.elements and '20 disclos'ed herein. .As-embodied in thepresentinvven-tion these wedging spring 'elements provide their failureto operate. Iieadzscreworjack actuating mechanisms of thisgeneral .typevare 4commonly used in; aircraft and other vehiclesyan'd `haveybeen.extensively utilized .for theeretraction of aircraft landinggears, floats,;bomb racks, tur- .rets and other components.`

In the operation of retractable:-aircraft-landing gears, binding `or.jamming at :the -leadscrew stops has frequently contributed .toiailureof the .actuating mechanism, and .inability v oi 'the pilot to extendhis .landing gea-r. These mechanisms 'are Iusually drivenbyanelectric,or fluid motor provided with a plate clutch which is permitted to slipwhen the nutelementstops against one of j.

the lead screw terminals. Suchsli-pping .of the clutch plateoccasionallycauses overheating and ywelding together of certain -of theplates' with the resultthat themotor outputshaft torquecan becomesuhicient to overcome .the locking torque and raise the wheel.. Inasmuchas the plate ,clutch isv then no longer capable of 'slipping andabsorbing. theinertia at the upper screwterminal 4,the high. resistance.to .the .motor torque-usually the motor is againl .energizedfor-extending the wheels .no torquev is. transmittedv through. thesheared clutch and'the-'landing.geariailsfto ex'- tend. Our invention,.consisting essentially -of "a low friction ball-typenutand lead screwvactuating mechanism .provided withfbeveled. ring stop assemblies at:each terminal of the lead. screw, and intermediate. ball thrust.bearings in. an improvedzrelationship,.entirely-elimnatesandzoverthediiilculties-.met with :in prior devices. .l

causes .shearing` oftheclutcl'l.l Accordingly, when ,f

The present'v invention isdirectedto anutrand lead screw combination ofrelatively low friction requiring-a .minimum of torque 'for its.yoperation, isl advantageously Iarranged. with '.wedging vspring elementsforming a tensional vand compressional friction bumper v.with 'an'interposed "ball thrust bearing. The ball 'thread actuating mechanismis of such low f'ricti'onal characteristics .as tof-be lcapable fo'ipermitting extension of "the .landing ygear `when acted upon only -by'gravitational yforces, `and the simplicity of construction, the

extreme compactness *and high capacity of the wedging spring'stopassemblies permits of va rel#- -ativeiy light, 'compact and eflicientlead screw `actuating mechanism. WhileV 'such beveled' ringAunitsfhavebeen proposed heretoforev as Ysubstitutes forv flexural"or'torsional springs, they have not heretofore been utilized totheir'complete ad; vantage in 'le'ad'screw mechanisms of the type L'loadcharacteristicsv of gradual or uniform thrust absorption with ya largeabsorption `oi energy.

v The disclosed arrangement of ab'eveled ring limit 'stop'in conjunctionwith a ball thrust'bearing-in a lead"scre'w `mechanism issuch `as tomaintain the value ofthe initial settings .under varying load andtemperature conditions. In addition to lits non-binding resilient thrustabsorbing qualities vthe presentv stop means' is comprised of .a minimumnumber of parts4 givingfool-proof and satisfactory service under Aalloperating conditions.

l Itis accordingl-ya-.major.object of .thepresent invention to provide.yan .improved limit .stop .means for lead screw actuating mechanisms. Ay.further purpose resides vin the provision of 4such va stopwhich'isnon-binding or jamming, which -is simple and of `low .costconstruction.. Another .objective Ylies inthe provision of limitstopmeans soil absorbing alarge part-of thewenergyexpended during itsbraking ofzthemovingparts. Aurther objective=.res-ides-in the ,provisionoi a new and `advantageous, combination .of :elements in a llead screwactuating mechanism including alow :friction ball type lead screw:threadiandxnut .of gsixch low nautiche-as to 'be capablefof' yextendinga landing gear when acted upon only by gravitational forces.

An additional object of the present invention is directed to theprovision of improved limit stop means which are capable of maintainingthe values of its initial settings under varying loads and temperatureconditions, and which may be used separately or in conjunction withconventional dog stops or other positive limiting stops of thenon-resilient type. Further objects and advantages of the presentinvention will become apparent to those skilled in the art after readingthe present description together with the accompanying drawings forminga part hereof, in which:

Fig. 1 is a cross sectional View of the improved lead screw actuatingassembly including the ball threaded nut member, the ball thrustbearings and the beveled ring terminal stops;

Fig. 2 is an enlarged part cross-sectional view i of the beveled ringstop means utilized therein; and

Fig. 3 is a graph illustrating the loading and unloading characteristicsof the improved stop means forming a part of this invention.

The screw actuating mechanism of Fig. 1 comprises the threaded leadscrew 5 lprovided with helical grooves or ball threads B extendingcontinuously through its intermediate portion to receive the frictionreducing spherical balls 'I. Beyond the threaded portion the lead screwmember 5 is provided with a lower or outer terminal portion 8 and anupper or main terminal portion 9. Adjacent its upper terminal :portionthere is provided a housing member I0 by means of which the lead screwassembly may be .pivotally or otherwise attached to the adjacentstructure in any one of a. number of well known manners and throughwhich housing I0 the lead screw 5 may be rotated for axial translationof the nut member II therealong. The nut member II is providedinternally with a continuous helical groove or ball thread I2 preferablyof like pitch and conformation as the thread 6 on the lead screw 5 toreceive the balls I therebetween. The nut element Il is also preferablyprovided with one or more spaces I3 within which a series of sphericalballs I4 are permitted to circulate to and from their positionsintermediate the inner face of the nut member and the outer face of thelead screw member.

The nut member II is shown fragmentarily in Fig. l for explanatorypurposes but it will be understood that this member may preferably be-provided with an elongated tubular portion, eX- tending toward theright in this figure, being of a diameter which will permit telescopingin an axial direction over the bearing portion of the llower terminal 8of the lead screw. The opposite end of the nut member Il is providedwith an end abutment 'face I5 against which the limit stop forces areexerted. The upper terminal portion `9 of the lead screw is ,providedwith an annular a, is retained upon the thrust bearing band 2| which isslidaibly fitted upon the cylindrical portion 9. The outer edge of theannular race 20 is beveled to engage the retainer element 20h whichserves to prevent the bearing I9, as well as the ring assembly 22, fromdropping out of place when the nut moves away from the bearing. Theentire assembly is preferably provided with a dust cover (not shown) toprotect the same from dirt and grit.

The beveled ring stop assembly 22 is comprised of a central annular unit23 of triangular section having an inside diameter which slidingly fitsupon the cylindrical upper terminal portion 3. As may be seen moreclearly in the detailed cross l section in Fig. 2 the upper surfaces 25of the triangular member 23 slope toward an apex at approximately a 15angle with respect to the axis of the cylindrical bore and have disposedthereon the complementarily faced outer annular elements 24. The wedgeelement 23 takes the form of a wide base isosceles triangle and thecomplementary elements 24 are preferably right angle triangles withtheir adjacent more acute angles cut on square at 34. In the normaluncompressed relationship of the elements 23 and 24 of the wedge ringstop assembly as shown in Figure 2 the outer elements 24 are separatedsuch that a space 34 exists between their inner edges, and their outeredges oVerlie the lateral edges of the inner central element 23 by thedistances indicated by the spaces 35.

It will accordingly be understood that the saparated and uncompressedrelationship of the wedge ring elements in Figure 2 is the same as thatoccupied by `the respective elements at the lower terminal portion 8 ofthe lead screw as shown in Figure l. Inasmuch as the nut II is shownfully compacted or retracted against the thrust bearing I9 and the stopassembly 22 at the upper terminal portion 9 of the lead screw theelements 23 and 24 in this figure are fully comrpressecl in the axialdirection between the inner abutment face I8 of the end bracket I6 andthe thrust bearing I9. In this fully compacted state the adjacent endsof the outer elements 24 are brought together occupying the space 34such that they abut in the region olf the apex of the inner centralelement 23, and the `outer edges of each element 24 become radiallyaligned with the corresponding outer edges of the central element 23. Asindicated above, the corresponding elements 23a and 24a of the outerstop assembly 30 are shown in their uncompressed relationship in Fig. l.

The compacting of the elements of the wedging spring assembly as shownat the upper terminal in Figure 1 results in the creation of compressionwithin the central element 23 and the tensioning of the outer element 24as a result of the deflection caused by the wedging action as theadjacent surfaces of each slide along the inclined wedging surfaces 25.Highly satisfactory results have been obtained from wedging elementsmade of steel although yother suitable materials may be used to obtainthe desired load characteristics. More resilient materials such asrubber composition and neoprene have been tested but Ihave not provensatisfactory in all applications, particularly at lower temperatures.

Using steel ring spring elements 23 and 24 a load characteristic ofgradual and substantially uniform thrust absorption was obtained whichat the same time provided a relatively large absorption of energy. IThese characteristics will be more clearly seen from the graph in'Figure 3 asomar 4in which; the .deflection is l/.iuooinch has been,plotted-against fthe load;in-.thousands1of pounds. :Itfwill be .notedthat .starting from .zeroload and deflection,v .obtaining inthe beveledvring stop -assembly 2-2 before. the face l 5. of the nut.` mem- :ber llimparts Vaxial movement. to thev thrust bearing I-Sand progressingthrough `tol-'the complete absorption of the'load, the load increases.quite uniformly asvthe deflection or c'oanpacting occurs and reaches lamaximum of approximately .12,500 pounds. at about .097 in. deflection.Thus the energy input to the stop 'assemblytis Vapproximately sents theyenergy absorption of the stop assembly. u

In this particular case it will be seen that the device has absorbed'some 60% of the energy expended up'on it. This lability to dissipatesubstantial amounts of' renergy makes'this device "particularlywellsuited for use asa. mitv stop.

-It will be understood that the 'nut member vIl is provided with asimilar but opposed abutment face corresponding to the `end face f5which is `adapted to bear against theinner face 29 of the fthrustbearing 28A vas the lead screw assembly is so "fully extended. Thiscauses similar' axial transmission of thrusts through thev bearing 28vto the 'lower stop assembly 30' vwhich is restrained lfrom outward axialmovement bythe 'end wall bracket '3l attached to the lower terminalportion B'by J the bolt 33. Movement of the assembly in the oppositedirection is prevented bythe annular band-21 and the shoulder 26.forming the end of the threaded portion'; The 'end wall bracket 3l maypreferably be provided with a bushing 3m over which the-innersurface ofa sleeve (not shown) forming a part .of the nut member Il may slide asthe screw mechanism is extended or retracted. The end bracket 3.1' mayfurther be providedwith a positive dog stop or clutch portion -32adapted to be engaged by a corresponding dog element on the nut memberIl to provide a positive nonresilient stop after full application of theload has :been applied to thev lower resilient stop assembly 13D, andafter the latter has been fully comipressed'.

By `means .of the .disclosed -ball thread nutand Alead screw,'thebeveled ring stop assemblies and ithe interposed ball thrustvbearing-s, .an improved 'lead .screw actuating mechanism has beenobtained which eliminates all of the aforementioned difliculties and hasproven "highly satisfactory under Aactual service conditions. Whilev 1.apreferred. embodiment of the present inventionlias been described inconnection with a screw mechanism of the rectilinear or push-pull typein which the sleeve of the nut member and the screw member telescope, itis not limited thereto, but is also adapted to be used with nut membershaving a pivotal connection adjacent the portion Il .andwviihoutatelescoping sleeve. The disclosed Lstop 'means is 4not limited to .usewith the ball- .bearing screw illustrated hereinbut also has 'been usedsuccessfully with a conventional .Acme 1 ,thread screw. In thisarrangement it serves an .additional function in .that it maintains anaxial load on the nut,v thus keeping the threads tightly' engaged andpreventing relative rotation between :the lnut and the screw asa result.of vibration. To vprovide this function it had formerly been .necessary.to use a synthetic rubber bumper.

VOther forms and modifications of thev present invention. both withrespect to the general ar'- .rangement as well as the details of therespective parts which may occur to those skilled in thezar't .afterreading .the foregoing description are all intended to come within thescope and spirit iof :this invention as more fully setA .forth intheappended claims.

We claim:

1. In a screw' retracting mechanism including :threadedinut and screwmembers arranged for relative vaxial movement upon rotation of' eitherimember, resilient stop means for limiting said axial movementcomprising a vplurality of telescopic annular elements havingcomplementary tapered friction `surfaces arranged to resiiently opposecompressive axial' forces and permit a reduction in the torque requiredvto reverse said .mechanismi 2. .Nut and 'screw actuating membersvhaving abutment shoulders carried bysaid nut. and screw members', aresilient vstop assembly disposed between said abutment shoulders ofsaid members comprising' an `inner beveled. ring and a pair o'f :outer:complementary beveled rings arranged to resiliently oppose `axialcompression with a uni- `form deflection under increasing compressiveloads-and arapid release of energy-absorbed from 'such. loads with arelatively small accompanying deflection.

3. A lead screw actuating mechanism comprising a threaded l:screwmember, a nut member 'threadedly 4engaging said screw member, reversibledriving means vfor imparting relative rotavtion between said members, anabutmentiixedly attached to said screw member. and an assembly ofbeveled annular rings interposed between said abutment and. said nutmember arranged to be axially compressed for the resilient limitation of,movement ofsaid nut member against said abutment. wherebythebrealr-away .reverse torque re- `quirements are reduced.

fl. A lead screwtactuatingmechanism comprising .a relatively rotatablethreaded screw member, a non-rotatable nut member threadedly engagingsaid screw member, means to rotate said screw member for axial movementof Asaid nut .member therealong, a transverse abutment carfried by saidscrew member, and stop means including a plurality of axially taperedLannular elem'ents interposed between said abutment and 'said nutmemberarranged to resiliently limit said relativera-idal movement of saidscrewand fnut members.

'5. A lead 'screw actuating mechanism comprisfing .a threaded rscrew.ymember, a threaded mit member co-axially disposed about said screwmember, said members having threads of semicircular cross-section, aplurality of spherical balls disposed within the threads of saidmembers, an abutment shoulder carried by said screw member and stopmeans including a plurality of 7 beveled ring elements co-axiallydisposed about limit axial movements of said screw and nut members.

6. A lead screw actuating mechanism comprising a threaded screw member,a threaded nut member coaxially engaged with said screw member, ashoulder portion carried by said screw member, a plurality of axiallytapered stop rings in wedging engagement disposed adjacent said shoulderportion and thrust .bearing means disposed between said stop rings andsaid nut member arranged to prevent transmission of rotation betweensaid stop rings and said nut member.

7. In a lead screw actuating mechanism, the combination of a rotatablemember and a member movable longitudinally thereof to dene a rectilinearstroke of fixed length, stop shoulders carried by the movable memberdisposed adjacent the opposite ends of said member to dene said strokelength, stop means carried by the rotatable member in a co-axialdisposition thereon, said stop means including an abutment memberiixedly attached to said rotatable member, a plurality of telescopicannular rings having complementary tapered friction faces, one of saidrings abutting said abutment member for the prevention of longitudinalmovement with respect to the axis of said rotatable member, l

bearing means carried by said rotatable member disposed between saidannular rings and the said rotatable member, whereby said telescopicannular rings are wedgingly and frictionally compressed between saidabutment member and said bearings means to resiliently absorb the axialforce caused by the engagement of the shoulder of said movable memberwith the stop means carried by said rotatable member and to materiallyreduce the torque required for the rotation of said rotatable member forbacking-01T said movable member.

8. Stop mechanism for a lead screw actuating device having a relativelyrotatable screw member and a non-rotatable nut member arranged fortranslatory axial movement therealong, said stop mechanism disposedbetween opposed portions oi said screw and nut members and comprising aplurality of telescopic annular rings having complementary taperedfriction faces arranged to permit axial compression of said stopmechanism between the opposed portions of said members upon approachingaxial movements and rapid release of the energy stored during said axialcompression for reduction in the breakaway torque required to reversethe relative axial movement between said screw and nut members.

9. A lead screw actuating mechanism including a threaded screw member, anut member threadedly engaging said screw member, said members havingaxially opposed abutment portions, and stop means including a pluralityof axially tapered ring elements disposed between the axially opposedabutment portions of said members arranged to resiliently limit relativeaxial movement therebetween and to provide for a rapid release of theenergy so absorbed at the limits of said relative axial movements.

10. In a lead screw actuating mechanism including a relatively rotatablescrew member havingr an abutment portion and a non-rotatable nut memberhaving an abutment portion arranged for translatory axial movement alongsaid screw member, a non-jamming stop assembly disposed between theabutment portions of said screw and nut members comprising a pluralityof telescopic annular rings having complemental tapered friction facesarranged to permit limited axial compression of said stop assemblybetween said abutment portions at the limit of said translatory axialmovement in a rst direction and the subsequent rapid release of theenergy stored during said axial compression upon movement of said nutmember in the opposite direction.

11. A lead screw actuating mechanism including a threaded screw member,a threaded nut member engageable with said screw member, means to rotateone of said members for axial movement along the other said member,transverse abutments carried by each said member, and stop meansincluding a plurality of axially tapered annular elements disposedbetween said abutments arranged to resiliently limit said relative axialmovement of said members.

12. Stop mechanism for a lead screw actuating device having a relativelyrotatable screw member and a non-rotatable nut member arranged fortranslatory axial movement therealong, abutment portions carried by eachsaid member, actuating means for rotating said screw member forimparting approaching and receding axial movements of said memberstoward and away from a limit position dened by said abutment portions,said stop mechanism disposed between said abutment portions carried bysaid members and including a plurality of telescopic annular ringshaving complementary tapered friction faces arranged to be axiallycompressed between said abutment portions upon approaching said liimtposition and to provide a rapid release of the energy stored during saidaxial compression for the reduction in the break-away torque required bysaid actuating means to reverse the rotation of said screw member toaccomplish the receding movement of said nut member from said limitposition.

FRANK TERDINA. WALLACE E. SKIDMORE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,656,279 Kreissig Jan. 17, 19281,908,655 Bell May 9, 1933 1,967,482 Schmidt July 24, 1934 1,984,565Bell Dec. 18, 1934 2,240,977 Bryant May 6, 1941 2297,137 Fennema Sept.29, 1942 2,398,841 `Morris Apr. 23, 1946 FOREIGN PATENTS Number CountryDate 630,555 France Dec. 5, 1927

